Hydrogen peroxide has been used as an oral rinse to support the healing of canker sores (aphthous ulcers), and its use is supported by some scientific evidence, though the strength of the evidence is moderate to low. Hydrogen peroxide acts as a mild antiseptic, releasing oxygen upon contact with tissue, which can help reduce the bacterial load in the mouth and may assist in cleaning the ulcer surface. This mechanism is hypothesized to promote a healthier environment for healing.

Several small clinical studies and reviews, such as those summarized in the Cochrane Database of Systematic Reviews (2012), have evaluated hydrogen peroxide and other mouth rinses for aphthous ulcers. The evidence suggests that hydrogen peroxide rinses may reduce discomfort and help in cleaning, but do not significantly speed healing compared to placebo or other treatments. Some guidelines and dental professionals recommend its use primarily for its cleansing effect rather than as a curative agent. Concentrations used are typically low (around 1.5% diluted from the standard 3% solution), as higher concentrations can be irritating or cytotoxic to oral tissues.

In summary, while hydrogen peroxide is not a cure for canker sores, its modest antiseptic and cleaning properties provide some rationale for its use as a supportive measure. However, the overall quality and quantity of evidence is limited, and its benefit appears to be minor.